Gas Injector

ABSTRACT

The invention relates to a gas burner or gas injector having a diffuser, which by control actuations can be modified within wide limits as a free jet burner and is suitable in particular for industrial furnaces with regenerative air preheating, in particular those which have an air supply arranged separately from the fuel gas. The gas injector according to the invention has a gas supply pipe  1  and a mouth  2 , wherein the connection thereof forms a long diffuser  3  with a free jet opening angle, and is characterised in that the ratio of the diameter of the mouth  2  and the diameter of the gas supply pipe  1  is smaller than three. Preferably a central nozzle pipe  4  with a mouth  8  forming a free jet opening angle is arranged within the gas supply pipe  1 , forming an annular gap  9  for guiding a partial gas flow between the gas supply pipe  1  and the central nozzle pipe  4 , in such a way that the notional prolongation of the generatrix  7  of the central nozzle pipe mouth  8  goes into the generatrix of the long diffuser  3 . A closure and regulating device is provided for regulating the partial flows.

The invention relates to a gas burner or gas injector having a diffuser,which by control actuations can be modified within wide limits as a freejet burner and is suitable in particular for industrial furnaces withregenerative air preheating, in particular those which have an airsupply arranged separately from the fuel gas.

It is known that primary NOx-reducing measures in relation toconventionally heated high temperature tank furnaces, in particular inrelation to glass melting tank furnaces, are particularly effective inrelation to the technology of introducing fuel. Admittedly major effortshave been undertaken in order to optimise furnace geometry and thedesign of the combustion air supply in terms of pollutant emissions, butnot least by virtue of the long installation service lives of more than10 years in which structural conditions are fixed, those measures areonly very late in taking effect, they are greatly limited in terms oftheir number and misguided developments can only be reversed after theend of the furnace campaign. It is also known that primary NOx-reducingmeasures, if technologically correctly applied, are linked to an energysaving, an increase in output, a prolongation of service life andquality assurance, but also require a degree of sensor system andintelligent automation as well as attentiveness on the part of theoperating personnel in order to maintain the high level attained inrespect of effectiveness and pollution reduction.

In accordance with the basic idea of NOx-reduction in relation to hightemperature processes like glass melting, DE 195 20 650 A1 disclosesburner-nozzle block combinations while DE 102 24 769 discloses free jetburners with an opening angle around 200 and a minimum mouth diameter of70 mm in a cylindrical burner insert bore without subsequently arrangednozzle block, which, by virtue of low-turbulence introduction of fuelgas, produce delayed mixing of fuel gas and combustion air and haveachieved acceptable NOx-reduction effects, with reduced flame roottemperatures in individual applications, with respect to the startinglevel.

Structures as in DE 102 24 769 do not have any possible ways of reactingto fluctuations in throughput in the typical output range but areequipped with turbulence-generating central nozzles which, bearingagainst the gas supply pipe internally, are operative only in theforward position and there cause rapid distancing from the NOx-reducingmode of operation. Solely reducing the cross-section of the diffuserroot is not sufficient to adapt the technologically required flame shapein direction and length to changed fuel throughputs.

With a low throughput the problem which arises is that the gas dischargespeed falls drastically, whereby the separately supplied combustion air,by virtue of its markedly higher impulsion and momentum, can interferewith the gas jet in such a way that the free jet characteristic is lostand the desired positioning of the flame in relation to the material tobe heated, which is determined by direction and length, can no longer beactively influenced. In an extreme case the combustion air sucks thefuel gas out of the injector mouth and the originally intended delayedmixing and starting reaction already starts directly at the breakawayedge of the combustion air supply. The advantage of the previously knownsolution, namely arranging the injector mouth without subsequentlyarranged burner nozzle block in the combustion chamber in order to avoidcontact of the intermittently supplied fuel gas with the refractorymaterial, as occurs in the construction of DE 195 20 650 A1, is thusnullified.

EP 0 513 414 B1 discloses apparatuses which provide for different flowconditions by means of axially displaceable conical nozzles directly atthe main discharge nozzle.

Solutions as in EP 0 513 414 B1 suffer from the disadvantage that thegas jet which is to be set with complicated and expensive conicalnozzles does not have the discharge paths which are required for optimumdelayed mixing, and the downstream-disposed nozzle block additionallycauses turbulence.

The technology of introducing fuel gas, relative to the air supply whichhas long been structurally fixed, suffers in the case of the knownsolutions from in part considerable disadvantages which give rise torisks in regard to the refractory material and thus the product qualityand the installation service life or which allow an NOx-reducing mode ofoperation in an only narrow range.

Thus the known solutions can no longer meet the increased demands interms of quality of heat transmission of the flame to the material to beheated, the degree of NOx reduction and the flexibility of firing of amodern production installation. With an increasing approach to thethermodynamic optimum of heat transfer and pollution reduction, there isan increasing need for simple, manageable and reproducible instruments,keeping that optimum stable and fully transforming the advantages intoeconomic and ecological benefits.

Therefore the object of the invention is to avoid the disadvantages ofthe known procedures but at the same time maintain the advantages of theundisturbed free jet with a simultaneous enlargement in the workingrange.

In accordance with the invention that object is attained by a gasinjector having the features of claim 1. Advantageous configurations ofthe invention are set forth in the appendant claims.

In that respect the concept of the invention in terms of the designconfiguration of the injector is based on the diameter ratio of thediffuser and the introduction of a double free jet procedure. With thenovel concept of closely restricting the diameter ratio of the mouth andthe feed pipe, it is possible in virtually every situation of use toimpart a low-turbulence free jet characteristic to the flow of gas in avery short time, without having to tolerate the above-mentioneddisadvantages. The characteristics of the long diffuser are notdetermined and limited by absolute dimensions of the mouth but representconditions in respect of the fuel gas supply, which are optimum in termsof flow technology, in wide ranges. Time-consuming trial-and-errorprocesses for determining the optimum operating point are eliminated andthe parameters can be easily transposed to other installations. In testswhich were conducted the running-in phases of several months could bereduced to a few weeks. In particular the risks to the refractorymaterial which can occur due to improved heat transfer and theaccompanying reduction in fuel throughput and reduction in the gasimpulsion and momentum are excluded. Adverse effects such as washing-outphenomena and surface spalling effects which only become apparent afterbetween 1 and 2 years can thus be avoided.

The invention is described in greater detail hereinafter by means of anembodiment with reference to the drawings in which:

FIG. 1 shows a lateral view in section of the front part of a gasinjector according to the invention which is fitted into a burner insertopening,

FIG. 2 shows a view in section through the entire gas injector accordingto the invention with a first embodiment of a closure and regulatingdevice, and

FIG. 3 shows a view in section through the entire gas injector accordingto the invention with a second embodiment of a closure and regulatingdevice.

FIG. 1 shows the position of a gas injector according to the inventionwhich is determined by the position of the mouth of a long diffuser 3 atthe end of a burner insert opening 6. The gas injector according to theinvention is provided with a gas supply pipe 1 and a mouth 2, whereinthe communication between the gas supply pipe 1 and the mouth 2 formsthe long diffuser 3 with a free jet opening angle. The configurationaccording to the invention of the long diffuser 3, determined by thediameter ratio of the gas supply pipe 1 and the mouth 2 which is lessthan three, ensures low-turbulence introduction of fuel in a wide rangeof uses.

The stability and flexibility of the low-turbulence fuel supply isenhanced to a high degree by the introduction of a second free jet inthe root of the diffuser 3. That is implemented by a central nozzle pipe4, the mouth of which is also in the form of a free jet opening angle,preferably of about 20°. The notional prolongation 7 of the generatrixof the mouth 8 of the central nozzle pipe 4 goes directly into thegeneratrix of the long diffuser 3. In that case the central nozzle pipe4 is preferably arranged in the gas supply pipe 1, providing an annulargap 9 between the central nozzle pipe 4 and the inside periphery of thegas supply pipe 1. Preferably there is also a closure and regulatingdevice 11 or 16 for regulating the partial flows through the centralnozzle pipe 4 and the annular gap 9. That permits an additionalmodification in the ratio of the partial flows through the centralnozzle pipe 4 and the annular gap 9 and permits the setting of alow-turbulence free jet at the most widely varying fuel throughput ratesas division of the partial flows occurs at such a distance relative tothe mouth 8 that both pass in a low-turbulence condition into the longdiffuser 3 and thus, in spite of differing input parameters, deploy thefull heat transfer efficiency and NOx-reduction effect.

The arrangement of a water-cooled ring 5 which protects the mouth 2which is mostly made entirely of metal and air-cooled from thermal wearalso has a stabilising and flexibility-enhancing effect. Cooling waterconnections 14 lead the coolant to the mouth region of the injector. Thewater-cooled ring 5 is closed by a partition between the feed and returnof the cooling water connection 14, whereby the cooling water flows oncethrough the hollow body of the ring and issues again. At the same timethe mouth cooling ring 5 forms an admittedly contact-free but closeclosure relative to the burner insert opening 6 and thus preventsunwanted ingress of infiltration air. The burner insert opening 6 ispreferably of a conically tapered configuration in the flow direction sothat vertical and horizontal angular deflection of the entire injectorin the free space 10 disposed therebehind becomes possible so that thedirection and position of the fuel free jet can be determined relativeto the incoming combustion air and relative to the material beingheated. The provision of a burner insert opening 6 which conicallytapers in the flow direction ensures and expands the specific use of thefree space 10 as an optimisation parameter without interfering with theoutflowing free jet, as is known from previous burner-nozzle blockcombinations. In order to ensure full availability of the free space 10for angular deflection of the injector, the water-cooled ring 5 ispreferably rotatable about the axis of the injector, whereby the coolingwater connection 14 can be respectively mounted in the part of the freespace 10, which is not involved in the angular deflection.

Division of the partial flows which is provided in accordance with apreferred embodiment in the central nozzle pipe 4 and the annular gap 9between the gas supply pipe 10 and the central nozzle pipe 4 can beeffected within or outside the gas supply pipe 1, with suitable closureand regulating devices being provided for that purpose.

FIG. 2 shows regulation within the gas supply pipe 1. Arranged betweenthe gas pipe 1 and the central nozzle pipe 4 is an axially displaceablecone 11 which co-operates with an inclined surface of the inside wall ofthe gas supply pipe 1 and which can regulate the annular gap 9 betweenthe two and in the extreme setting completely close it. Axialdisplacement of the cone 11 can be effected by way of a spindle 12 orother suitable devices which are set in movement by a spindle drive 13.Complete closure of the annular gap 9 represents the lower working pointof the injector, that is to say 100% of the gas flow flows through thecentral nozzle pipe 4. Complete opening of the annular gap 9 byretraction of the cone 11 in opposite relation to the flow directionrepresents the upper working point with full fuel throughput. Theintermediate positions can be steplessly set by displacement of the cone11.

In the second case which is shown in FIG. 3 the overall gas flow isdivided by conduit means before passing into the gas supply pipe 1. Asecondary gas supply pipe 15 branches off an overall gas supply 17 whichopens into the gas supply pipe 1, and directly charges the centralnozzle pipe 4. Disposed in each of the two supply conduits is a valve 16for adjusting the respective partial gas flow. Both partial flows, boththat through the annular gap 9 and also that through the central nozzlepipe 4, can be 100% shut off by the separately arranged valves 16 andcan be steplessly adjusted therebetween. Other closure and regulatingdevices are possible.

LIST OF REFERENCES USED

-   1 gas supply pipe-   2 mouth long diffuser-   3 long diffuser-   4 central nozzle pipe-   5 water-cooled ring-   6 burner insert opening-   7 notional prolongation of the generatrix of the central nozzle pipe-   8 mouth central nozzle pipe-   9 annular gap-   10 free space-   11 cone-   12 spindle-   13 spindle drive-   14 cooling water connection-   15 secondary gas supply pipe-   16 valve-   17 overall gas supply

1. A gas injector for nitrogen oxide-reducing firing of regenerativelyheated industrial furnaces comprising a gas supply pipe and a mouth,wherein the connection thereof forms a long diffusers with a free jetopening angle, characterised in that the ratio of the diameter of themouth and the diameter of the gas supply pipe is smaller than three.2.-10. (canceled)
 11. A gas injector as set forth in claim 1characterised in that a central nozzle pipe with a mouth forming a freejet opening angle is arranged within the gas supply pipe, forming anannular gap for guiding a partial gas flow between the gas supply pipeand the central nozzle pipe, in such a way that the notionalprolongation of the generatrix of the central nozzle pipe mouth goesinto the generatrix of the long diffuser.
 12. A gas injector as setforth in claim 11 characterised in that a closure and regulating devicefor partial gas flow adjustment is arranged downstream of the centralnozzle pipe.
 13. A gas injector as set forth in claim 12 characterisedin that the closure device comprises two separate valves which arearranged in an overall gas supply pipe and a secondary gas supply pipewhich is branched therefrom and which directly charges the centralnozzle pipe.
 14. A gas injector as set forth in claim 11 characterisedin that the closure device is in the form of a cone which is axiallydisplaceable on the outer periphery of the central nozzle pipe and whichco-operates with a conical surface of the inside wall of the gas supplypipe.
 15. A gas injector as set forth in claim 12 characterised in thatthe closure device is arranged set back in opposite relationship to theflow direction from the mouth of the central nozzle pipe by more thanfive times the inside diameter of the central nozzle pipe.
 16. A gasinjector as set forth in claim 14 characterised in that the closuredevice is arranged set back in opposite relationship to the flowdirection from the mouth of the central nozzle pipe by more than fivetimes the inside diameter of the central nozzle pipe.
 17. A gas injectoras set forth in claim 1 characterised in that the mouth of the longdiffuser is provided with a water-cooled ring at its outside periphery.18. A gas injector as set forth in claim 17 characterised in that thewater-cooled ring is arranged separately.
 19. A gas injector as setforth in claim 17 characterised in that the water-cooled ring isrotatable about the axis of the gas injector.
 20. A gas injector as setforth in one or more of the preceding claims characterised in that thelong diffuser and the ring are arranged together in a burner insertopening enlarging in opposite relationship to the gas flow direction, insuch a way that the spacing between the water-cooled ring and the burnerinsert opening is at a minimum and the axis of the gas injector isrotatable about the center point of the mouth.